Large, metal carrier rolls are widely used in paper making and non-woven fabric lines to convey and/or drive the paper or fabric stock or conveyor belts supporting the stock. These rolls have a variety of names depending upon their particular operation and location in the lines. These include wire rolls, table rolls, paper rolls, carrying rolls, blow rolls, felt rolls (dry or wet), drive rolls (wire, felt or dryer felt), head rolls, tail rolls, etc.
Common characteristics of these rolls are that they are relatively large, typically having outer diameter; of about six inches to about eighteen or more inches, lengths cf about five feet to about twenty-five or more feet and masses of about 200 to about 12,000 or more pounds. Maximum surface speeds of such rolls might range from about 160 feet per minute for the smallest diameter rolls to about 5,000 feet per minute for the larger diameter rolls.
The carrier rolls in question are further distinguished from press rolls, which are of a much heavier construction. Typically, press rolls are loaded in operation from about 100 to about 3,000 or more pounds per linear inch of axial length of the roll. The carrier rolls to which the present invention is directed are subjected to lesser loads. In paper making, the loading on carrier rolls during operation is less than about 100 pounds per linear inch.
A number of methods have previously been employed to fabricate the large, metal carrier rolls to which the present invention is directed. Such rolls typically comprise a hollow, generally cylindrical metal body having a pair of open axial ends each of which contains a metal end head supporting a journal. One prior method of fabricating such rolls has been to install an axially elongated piece of cylindrical metal stock in each open axial end of the body and machine an end of the stock protruding from the body into a journal. Another method has been to install a machined journal shaft through an annular metal end head, mount the end head with journal shaft in an open axial end of the body and thereafter turn and balance the body.
Regardless of the methods previously employed to fabricate the rolls, it has always been a requirement that the rolls be balanced to within a predetermined residual unbalance value for rotation up to a predetermined maximum service speed for the roll. During balancing, such rolls would be supported on their journals in a dynamic balancing machine and rotated on the journals to determine the state of balance of the roll. Thereafter, conventional steps such as the removal of metal by drilling are performed on the roll to bring it within an allowable residual unbalance value for rotation up to the predetermined maximum service speed.
Major problems arise for the roll users when such rolls must be repaired. Spare rolls are typically not stocked by or the manufacturer and often are not stocked by the user. When a roll needs to be repaired, the entire manufacturing line must be stopped while the roll is removed from operational service. If a spare roll is available, it can be installed. Otherwise the line remains down while the damaged roll is repaired, rebalanced and reinstalled. While it may be possible to actually repair a roll on the spot, balancing machines to rebalance the roll are typically only available at the roll manufacturing facilities. Depending on the severity of the roll failure, the rolls may have to be removed from the manufacturing site, transported back to the manufacturing facility for repair, rebalancing or both before being returned to the manufacturing site for reinstallation. While such instances of roll repair are not frequent, they can be extremely and even catastrophically destructive to the operation and business of the roll user.
It would therefore be very useful to provide rolls which are capable of being repaired on site and immediately returned to operational service with a minimum dow time of the line in which the roll is installed.
There are no absolute requirements for the amount of residual imbalance which is permissible in such carrier rolls. Individual users may specify permissible residual imbalances for their rolls based upon special requirements. Where permissible residual unbalances are not specified, it is widely the practice in the industry to balance the rolls to within a Balance Quality Grade G-6.3 residual unbalance value as defined in Acoustical Society of America Standard 2-1975 for "Balance Quality of Rotating Rigid Bodies". This standard has also been approved by the American National Standards Institute as standard ANSI S2.19-1975.